In recent years, the number of reports of work-related musculoskeletal disorders such as cumulative trauma disorders (CTDs) (also called repetitive stress injuries (RSIs)) has multiplied. Some risk factors which contribute to the development of RSIs include applied force, acceleration, velocity and repetition rate of a task. A common RSI is carpal tunnel syndrome, a condition characterized by a thickening of the protective sheaths which surround each tendon in the wrist which control finger movement. Carpal tunnel syndrome may be caused by repetitive flexing and extension of the wrist.
Workers are susceptible to injury from the sustained repetitive activities which define some jobs. Typing is an example of a job which requires a person to perform the same motion pattern every few seconds, as are jobs which require the use of vibrating equipment, and jobs in which workers repeatedly handle heavy objects.
Increasingly, employers are examining those jobs and workpieces that have risk factors for RSIs to determine the extent to which RSIs or the potential for RSIs are present. It is therefore desirable to identify the movements or stresses on each job or within each workpiece which may present patterns of harmful physical stress, and to quantitatively measure and analyze the levels of physical stress while the potentially harmful activity is being performed.
A variety of biofeedback devices are available to aid in gathering data pertaining to musculoskeletal stresses. For example, electromyographic sensors and force sensing resistors measure muscular activity and force, respectively, and position sensors measure posture. Typically, biofeedback units utilize one type of device to translate a particular physical activity of a person into electric signals, and display representations of the signals in understandable form to the person whose activity is being monitored.
One type of well known biofeedback unit measures electromyographic (EMG) activity, that is, the electrical activity of a muscle during contraction, via electrodes placed on the skin over a muscle or a group of muscles to be monitored. Another kind of biofeedback unit, a goniometer, provides feedback regarding the angular position of a joint of the human body, i.e., posture. It is further widely known to sense vibrations by attaching accelerometers to parts of the body, and to sense levels of force between a portion of a person's body, such as the fingertips, and another object, such as a keyboard, with variable force sensing resistors (FSRs). EMG electrodes, goniometers, accelerometers, and FSRs are all items which are available off-the-shelf from various sources.
Portable biofeedback systems which are capable of gathering multiple types of musculoskeletal stress data simultaneously, however, have not heretofore been available. A biofeedback unit for measuring, for example, pressure, muscle activity and posture simultaneously offers the advantage that a researcher may determine at a glance the muscle effort and posture required to sustain a specific force during performance of a task.
In addition, it is awkward and time consuming to utilize separate portable units to measure more than one type of activity, and many biofeedback systems require a user to perform extensive and complicated calibration procedures before each use--such systems are generally not suitable for use at a worksite to measure on-the-job musculoskeletal stresses, nor are they useful to quickly test the ergonomics and/or efficacy of a workpiece's design.
Advantages and novel features of the invention will be set forth in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.